1. Field of the Invention
The invention relates to a numerical control (NC) unit provided with an ultrasonically oscillating tool capable of forming an iridescent face (like, for example, a CD face with a track of pits indented thereon) directly on the surface of a die by, for example, applying micro-indentation treatment to the die.
2. Description of the Related Art
The configuration of a conventional NC unit provided with an ultrasonically oscillating tool is described with reference to FIGS. 2 to 4. The NC unit is in principle not affected by the number of axes, and may be of a .theta.-axis control type, however, for convenience of description, an orthogonal biaxial NC unit is described hereinafter as a typical example.
In FIG. 2, reference numeral 1 denotes an X-axis motor, 2 a Y-axis motor, 3 an X-axis pole thread, 4 a Y-axis pole thread, 6 an ultrasonically oscillating tool, and 7 a work piece to be processed (referred to hereafter as a work).
The ultrasonically oscillating tool 6 is mounted so as to be able to travel on the X-axis pole thread 3, and indents pits on the surface of the work 7 through interpolative control by the Y-axis motor 2 and the X-axis motor 1 traveling on the Y-axis pole thread 4.
A conventional oscillation control circuit for the ultrasonically oscillating tool 6 is described with reference to FIG. 3, and a conventional driving circuit for driving the X-axis motor 1 and the Y-axis motor 2 is described with reference to FIG. 4.
In FIG. 3, reference numeral 11 denotes an oscillation circuit for generating an ultrasonic signal 12 an amplifier circuit, 13 a matching circuit for impedance matching, 6 the ultrasonically oscillating tool, 15 a piezoelectric element, 16 a horn, and 17 a stylus.
The signal generated by the oscillation circuit 11 is amplified in the amplifier circuit 12, and via the matching circuit, causes the piezoelectric element 15 to be oscillated. At this point in time, if the piezoelectric element 15 is oscillated at frequency f satisfying the following expression: EQU f=C/4L
where C is specific acoustic impedance determined by the horn 16 and the stylus 17, and L is the whole length from the top of the horn to the tip of the stylus, ultrasonic oscillation occurs to the ultrasonically oscillating tool 6 due to the effect of resonant relationship.
In FIG. 4, reference numeral 21 denotes a CPU (central processing unit), 22 a DPU (dual port memory), 23 an interpolative operation circuit, 24 an FGC (function generator: frequency modulator), 25 a sensor input circuit, 26 a control output circuit, 27,28 servoamplifiers, 1,2 the motors described with reference to FIG. 2, and 30, 31 rotation sensors for outputting pulses in number proportional to the rotation angle of the motors 1, and 2, respectively.
With the configuration described above, coordinate data written to the DPM 22 by the CPU 21 is processed for interpolative operation by the interpolative operation circuit 23, and outputted to the control output circuit 26 at a timing synchronized with a synchronous pulse CP outputted from the FGC 24.
The control output circuit 26 generates a motor driving signal based on an output of the interpolative operation circuit 23, and sends out the same to the servoamplifiers 27, 28 at a timing according to the synchronous pulse CP. This causes the motors 1, 2 to be driven for rotation. A rotation angle of the motors 1, 2, respectively, is detected by the rotation sensors 30, 31, and an output of the rotation sensors 30, 31, respectively, is fed back to the servoamplifiers 27, 28, and simultaneously delivered to the sensor input circuit 25. The sensor input circuit 25, upon receiving the outputs of the rotation sensors 30, 31, sends out rotation angle signals based on the outputs to the interpolative operation circuit 23. The interpolative operation circuit 23 recognizes the present location of the ultrasonically oscillating tool 6 from the outputs of the sensor input circuit 25.
With the conventional NC unit provided with the ultrasonically oscillating tool, the circuits (in FIG. 3) for driving the ultrasonically oscillating tool 6 are asynchronous with the circuits (in FIG. 4) for causing the same to travel, and consequently, pits could not be indented at identical pitches as shown in FIGS. 5(A) and 5(B) when an ultrasonic processing is applied to the work, causing an undesirable problem particularly when a process for forming an iridescent face is applied.
Further, with the conventional unit described above, any shift in resonant frequency, if and when occurs due to wear and tear of the stylus 17, could not be detected, causing a problem of faulty oscillation after use thereof over many hours.